A group of treated and control tagged honeybees at release time. Photo © Science/AAAS

Two new studies link systemic insecticides to declining bee health

A group of treated and control tagged honeybees at release time. Photo © Science/AAAS

Two scientific studies of the effect of neonicotinoid insecticides on honey bees and native bumblebees are adding more weight to the belief that these systemic chemicals are greatly responsible for the decline in worldwide bee health.
Beekeepers who are already tuned in to the understanding that pesticide residues found in wax foundation affect hive health therefore won’t be surprised to learn that researchers in France and the United Kingdom are linking this common crop pesticide with harmful effects on bees, from loss of forager orientation to weakened colonies and a loss of fecundity in queens.
The two reports were published online this week by the prestigious journal Science and immediately gained worldwide attention.
The studies show that “neonics”, which have grown dramatically in use since their invention in the 1990’s, have widespread effect on both native and non-native pollinators.
The chemicals are applied as a dip for crop seeds, with the result that the insecticide is distributed throughout the growing plant, including nectar. Bees collecting that nectar and affected pollen then take it back to their colonies, where the residues are believed by some scientists to result in low-level toxicity, the long-term effects of which are still in dispute.

Honey bees equipped with micro radio transmitters. Photo © Science/AAAS

In the French experiment, led by Mickael Henry of the French National Institute for Agricultural Research, researchers tagged free-ranging honeybees with micro-transmitters and then fed some colonies a sub-lethal does of the pesticide thiamethoxam. (This systemic insecticide was developed by Syngenta but German chemical giant Bayer Cropscience, which holds the patent for neonics, sued them. In 2002 Syngenta settled, paying Bayer $120 million for worldwide rights to thiamethoxam.)
Henry’s team discovered bees exposed to thamethoxam were two to three times more likely to die away from their nests, likely because the pesticide interfered with their homing system.
In the bumblebee experiment, Penelope Whitehorn, Dave Goulsonand other colleagues at the University of Stirling in the UK exposed bumblebees, Bombus terrestris , to Bayer’s  neonic imidacloprid. The doses were apparently comparable to what bees are exposed to in the wild, and researchers then monitored their health over a six week period. They found the exposed colonies were on average up to 12 per cent smaller than control colonies located nearby. Strikingly, they also found that they also produced 85 per cent fewer queens.

A moss carder bumblebee, Bombus muscorum. Photo © Science/AAAS

Given that bumblebee queens winter as solitary bees, this meant that there would be 85 per cent fewer nests the following year.
Not surprisingly the folks over at Bayer aren’t convinced with the results of the two studies. David Fischer, an ecotoxicologist with the company, told The New York Times the studies were flawed. He suggested the French researchers gave the honeybees an unrealistic amount of neonics. “I think they selected an improper dose level,” he told The Times
Others have also raised questions about the studies’ conclusions. But equally, some scientists who have been studying the effect of neonicotinoids on pollinator health say the results are alarming.
But neonics have for a long time been thought to be a contributing factor to that mystery, “colony collapse disorder”. Certainly that has been the view of David Hackenberg, the commercial US beekeeper who first discovered CCD in 2006 when he found bees had disappeared from 400 of his Florida hives. Since then the phenomenon has struck deeply at beekeepers across North America and Europe.
While the actual cause of CCD is not understood, scientists and beekeepers increasingly suspect that it is a combination of problems, from neonics to the effects of pesticides in wax to mites and viruses. The combination of any two of those may be enough to tip hive health off the shelf.
Neonics have been suspected of affecting honey bees for years, leading several European countries, including France, Italy and Germany, to suspend the pesticides. The latest two studies likely will only harden that resolve.
In the U.S., environmentalists were quick to point out that these studies may also give the U.S. Environmental Protection Agency enough ammunition to reconsider registration of Bayer’s products. Tom Philpott at Mother Jones wrote this provocative post in which he noted that the EPA had approved some Bayer products based on the company’s own studies, which were later discredited by EPA staff.
Alison Benjamin, the author of A World Without Bees, argues in The Guardian that the two studies now show beyond a shadow of a doubt that neonics are deadly to bees.
To be sure, these two studies aren’t the first forays into research around the effect of insecticides on honey bees, There’s an impressive list of reference studies attached to these the French and UK work that show for researchers have been concerned for years about the growing effect of chemicals on insect health. When I get a chance I will post that bibliography to this blog.

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